嗨,我正在尝试在树视图中实现数据库记录,如父(表)和子(表)。在运行期间,我的连接字符串中出现错误。string connectionstring = ConfigurationManager.ConnectionStrings["Data Source=ASDF;Initial Catalog=dbtree;Integrated Security=True"].ConnectionString;System.NullReferenceException was unhandled by user code
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